Terra has been with me for about 10 days - rescued from a pretty bad situation. I probably should have asked about this earlier.

she has a little, sort of milky white spot on the back of her neck, about the size of her eye (she's 4"). I might have thought it was just a part of her coloring, except she was also missing a claw when I got her, and there is similar coloration around the missing claw (which seems to be growing back.

I'm worried it's some kind of infection. Is there any sort of first aid I can apply? Does this sound familiar to anyone?

my turtle had that too. i was told it was the scar tissue thing like meg said.

but i think my turtle had a small infection. i tried salt and that sulfa dip, but i'm not sure it helped or not. i'd hold off on the sulfa dip and maybe try some salt on it.

one day i was just touching it and he moved his neck and it got caught under my nail and it just came off! there was a little indent where it was.
then it grew back the next day and then fell off again and never grew back.

i never really did anything, except moved the uvb light closer and got a better filter
i'll see if i can find a pic of when my turtle had it.

Don't know about the missing pic, but if the turtle was kept with others, it could be a bite mark (especially with the missing claw). If it is, the areas will be white if the turtle has been in the water for a while. You could apply an antibiotic ointment (Neosporin) to the areas and keep the turtle out of the water overnight. Do this for several days and see if there's any improvement.

"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-

The thing is, there's this yellow dot at the center of the cloudy spot, and I don't know if it's an infected wound or just a yellow dot. In this photo you actually can see the dot more than the milky spot, but from most angles, it just looks like a bit white blotch on her neck...

Do me a favor, put on some thin plastic gloves but still wash your hands after. Gently feel it to see if there is retained fluid build up or if it is firm. I may be able to tell by a photo but it does sound like a exotic or herp vet may be your best bet in this case. Now if it is scar tissue, you could tend to it yourself but with you pointing out the different coloration, it could be a variety of things anywhere from a internal parasitic issue to a bacterial infection of some sort which would need to be determined by a vet on which one it is. A fluid build up would identify the parasitic issue or a bacterial infection and if it is firm, it could be a old or recent injury. What ever you do, if it is a fluid build up of any kind, do not press it with force as you don't want the chance of it getting deep into your turtle child's bloodstream giving the prescribed vets medication the opportunity to attack a infection from the deep inside towards the outside skin surface if this makes sense. Good luck with your turtle child and feel free to message me anytime.